1. FIELD OF THE INVENTION
The present invention pertains to surface coating materials for glass surfaces. In particular, the present invention relates to a process for improving the scratch resistance and labelability of glass surfaces. A particular aspect of this invention relates to improved abrasion-resistant glass coatings which are label receptive and possess good printability without further treatment.
Glass derives its considerable strength from an unblemished pristine surface and any scratches or flaws which are present on its surface decrease its strength to a fraction of its original value. Generally, glass containers such as jars, bottles and tumblers, and the like, exhibit maximum strength immediately upon forming, and this strength decreases as the containers come into contact with each other and with other surfaces in the course of manufacturing, filling, packaging and shipping.
After glass surfaces are coated with a composition having good wet and dry scratch and abrasion resistance properties, which by imparting such scratch resistance decreases the likelihood of breakage, more glass containers can be handled by the filling and packaging apparatus in the same amount of time by spacing the containers closer together and increasing the speed of the article handling conveyors even though the glass surfaces will be subject to more contact with other surfaces. Since many products are packaged under pressure, such as beer and carbonated beverages, it is highly desirable that the surfaces of glass containers possess as few scratches as possible to minimize or prevent the possibility of breakage.
It is known in the art that if the glass surfaces are coated with a composition which exhibits such abrasion-resistance and to which labels readily adhere, and also which possess good printability without further treatment, such compositions would represent a substantial contribution to the art.
2. DESCRIPTION OF PRIOR ART
Worthwhile attempts have been made in the past to increase the strength of glass containers by coating their exterior surfaces with a polyethylene coating. While polyethylene does produce a good essentially-transparent coating, its inherent hydrophobic nature makes it a poor surface for adhering labels, inks and decorations. It has been found that by using selected copolymers which possess increased polarity in reference to the respective monomer, it is possible to overcome the disadvantages associated with the prior art, that is the mixture of particular organic resins or polymers employed herein increase the scratch resistance of the glass surfaces which are also more receptive to the adherence of printing inks and labels.
U.S. Pat. No. 2,995,533 to Parmer and Schaefer, issued Aug. 8, 1961, entitled, "Lubricant Coating For Glassware", and U.S. Pat. No. 3,554,787 to Plymale, issued Jan. 12, 1971, entitled "Glass Articles Having Dual Scratch And Abrasion Resistant Coating And Method For Producing Same", assigned to the same common assignee as the present application, relate to glass surface coatings which involve single and dual coatings of polymers, respectively. The former discloses the use of polyethylene emulsion as a lubricant coating, while the latter discloses a tin or titanium oxide first coating which is overcoated with a second coating of organic copolymers. Both of these disclosures involve coatings which are abrasion resistant but which have experienced labeling problems.
Other patents which relate to glass surface coatings are the following: U.S. Pat. Nos. 3,323,889 and 3,368,915 to Carl and Steigelman relate to abrasion-resistant glass articles having dual protective coatings and method of forming same. Also, U.S. Pat. Nos. 3,414,429, 3,598,632 and 3,418,154 all relate to methods of rendering glass surfaces abrasion resistant; however, all are devoid of teachings which in addition provide the surfaces with good label adhesion and printability. Also, all of the above-listed patents are originally assigned to the same assignee as the present application.